Directional Modulation With Precise Legitimate Location Using Time-Modulation Retrodirective Frequency Diversity Array for Secure IoT Communications

Designing energy-efficient security techniques for Internet of Things (IoT) networks is particularly vital due to its limited battery capacity and the flow of information via broadcasting. In this article, we propose retrodirective frequency diversity array (RDFDA) based on directional modulation (DM) concept in a time-modulated way to enhance security in IoT. Different from the existing IoT security, in the proposed scheme, the prior knowledge of the intended receivers' location is not required for the transmitter and no need of channel state information. Leveraging on this feature, we design time controlling switch sequences, which require a single radio frequency chain. To facilitate the DM operation in the proposed RDFDA, the connecting-disconnecting switching functionality for each element branch needs to be judiciously selected. Furthermore, we give insights on how the useful messages can be leaked along the eavesdropper (Eve) direction when an outage has occurred as well as Eve error detectability by analyzing the following metrics such as secrecy outage probability, Eve detecting error probability, and leakage rate of noncolluding Eves. Other metrics, such as secrecy energy efficiency, economic efficiency, and cost efficiency were also analyzed. We give numerical results to disclose the proposed scheme achievements.